| Mechanisms and predictions of water and nutrient transportation in soils at a slope during rainfall have been playing important roles in the research on the degradation of soil quality and the expansion of non-point source polution in recent years, which also have been an interdisciplinary field focused in soil erosion, hillslope hydrology, dryland agriculture and related environment science. And raindrop kinetic energy and slope are recognised as the most significant factor causing water erosion and nutrient transportation. Describing the transport rules of soil water and solute scientifically and determining their transport characters and related parameters can provide data support for establishing prediction and forecast models of soil water and solute transport. And it is also important for soil water management and agriculture eco-environment protection.In this dissertation, the effects of raindrop kinetic energy, gradient and solute application positions on the migration mechanism of soil, water and solute on the slope land were studied by the methods of simulated rainfall experiments taking red soil in the south of China as the object. The purpose of this study is to provide the basis for the movement of soil water in red region and the rational utilization of soil and water resources. The main conclusions in this paper are follows:1. The relationship. conformed by adopting the method of the stain on the filter paper produced by the raindrop through the cotton thread, between the raindrop’s diameter and the stain’s diameter is d=0.4434D0.6589. The results showed that the raindrops’diameter of the test area range from0.443mm to2.755mm, and they are in normal range of raindrop’s diameter (100um-3.5mm).And The kinetic energy of each rainfall is calculated by the formula of kinetic energy, The results of calculation showed that the rainfall energy of the test area range from0.036J to2.047J.2. Moisture content of the soil surface, infiltration depth and the time of beginning to form flowing water decreased with the increasing of the kinetic energy of raindrop. When the raindrops’kinetic energy came to zero, the slope of the red soil almost had no runoff. Whatever the size of the kinetic energy was, the intensity of runoff on the slope of red soil showed a linear change with time, but the growth rate of the-runoff intensity growed with the increasing of kinetic energy. Thus the total amount of runoff had a trend to increase as the kinetic energy increases. When the kinetic energy added up, the amount of sediment of runoff also increased, but there was a limitation of effect of kinetic energy to the erosion. The energy of raindrop had no significant effect on the variation of the bromide cations’ concentration of slope runoff of the red soil, it was obeseverd that bromide concentration decreased in a power function with time. With the increasing of kinetic energy, the total amount of bromide ion loss in the runoff was gradually increasing. The DP concentration of runoff showed a wavy changing process with the time of rainfall, and during the process of rainfall, instead of the kinetic energy of raindrop was2.45J, raindrops’kinetic energy under other conditions had a significant concentration peak, what’s more, the larger the kinetic energy was, the higher the DP concentration in the same periods of rainfall. The total amount of TP losses in runoff increased with an increasing kinetic energy, consistenting with the total amount of runoff and the volume of sediment in runoff. After the rainfall stopped, the leaching depth of the non-adsorbed solute (bromide ions) added up with the kinetic energy increasing, and phosphorus which has strong adsorption was concentrated in the surface layer within5cm layer.3.The runoff in the first raindfall had significant characteristics with time-varying, and it was latest and had the least erosion; On the other hand,the second and third rainfall changed with the surface erodibility, so the erosion increase, the erosion of the first and second rainfall is1/7、1/2of the third rainfall. The solute of different cast parts had little effect on variation of the concentration of Br-, the changes of concentration of solute can be represented with exponential. At the condition of fertilization under the slope, the initial concentration of Br-in the runoff was highest, and also its’attenuation was fastest. The runoff during the late rainfall, the sediment yielding and solute transportation had effect on the soil physical conditions during the earlier rainfall and the solute distribution characteristics. At the condition of fertilizating on the slope, the solute leached into the soil has the most opportunity to participate in the runoff once again, and the total losses of solute are max.4. The variations of runoff rate with time for different gradients on red soil slopes were described by linear functions. The rate of increment of runoff rate reduced with an increasing slope gradient. Total volume of runoff decreases linearly with increasing gradient. There was a critical slope gradient existed for red soil erosion process according to the relationship of the sediment loss and slope gradient affected. The decay processes of Bromine concentrations in runoff were the best described by a power function for different slope gradients. The dissolved phosphorous (DP) loss in runoff mainly caused by runoff. It could be determined preliminarily that the critical slope gradients for the least loss of solution is approximate15°according to the relationship between solution loss and gradients. The Br’leaching depth in soil profile increased with an increasing slope and the soil extracted phosphorous distributed mainly in the soil profile of5cm in depth after simulating rainfall. |
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